Optical film piece and method for manufacturing the same

Abstract

To provide an optical film piece which can reduce the weight of a VR goggle while improving the visibility.SOLUTION: An optical film piece 1 has an absorption-type polarization film. The absorption-type polarization film is formed of polyvinyl alcohol resin. In the main surface of the absorption-type polarization film, the orientation function of a first site 28c located in the center part is different from that of a second site 28d located outside the first side 28c.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to optical film pieces and methods for making the same. [Background technology]

[0002] Image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices), are rapidly becoming widespread. In image display devices, optical members such as polarizing members and phase difference members are generally used to realize image display and to improve the performance of the image display (see, for example, Patent Document 1).

[0003] In recent years, new applications for image display devices have been developed. For example, goggles with displays (VR goggles) for realizing Virtual Reality (VR) have begun to be commercialized. Since VR goggles are being considered for use in various situations, there is a demand for them to be lightweight and have improved visibility. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-103286 A Summary of the Invention [Problem to be solved by the invention]

[0005] The weight of the VR goggles can be reduced by, for example, thinning the lenses used in the VR goggles. On the other hand, there is a demand for the development of optical members suitable for display systems using thin lenses.

[0006] In view of the above, a primary object of the present invention is to provide an optical film piece that can effectively achieve weight reduction of VR goggles while improving visibility. [Means for solving the problem]

[0007] 1. An optical film piece according to an embodiment of the present invention is an optical film piece comprising an absorptive polarizing film, the absorptive polarizing film being made of a polyvinyl alcohol-based resin, and on a main surface of the absorptive polarizing film, an orientation function of a first portion located at the center is different from an orientation function of a second portion located outside the first portion. 2. In the optical film piece described in 1 above, the absorptive polarizing film may have a portion having an orientation function of 0.30 or less. 3. In the piece of optical film according to the above 1 or 2, the absolute value of the difference between the orientation function of the first region and the orientation function of the second region may be 0.02 or more. 4. The optical film piece according to any one of 1 to 3 above may have a curved main surface. 5. A method for producing an optical film piece according to an embodiment of the present invention is a method for producing an optical film piece as described in any one of 1 to 4 above, which includes heating and stretching a member including a polyvinyl alcohol-based resin film to integrate it with a part having a curved surface, and the orientation function of the polyvinyl alcohol-based resin film is 0.30 or less. 6. In the method for producing an optical film piece as described in 5 above, the curved surface of the component may have a radius of curvature of 150 mm or less. 7. In the method for producing an optical film piece as described in 5 or 6 above, the curved surface of the part may have a radius of curvature of 40 mm or less. Effect of the Invention

[0008] According to the optical film piece according to the embodiment of the present invention, it is possible to effectively achieve a reduction in the weight of the VR goggles while improving the visibility. [Brief description of the drawings]

[0009] [Figure 1] 1 is a top view of a piece of optical film according to one embodiment of the present invention. [Diagram 2] 2 is a schematic enlarged partial cross-sectional view showing a general configuration of the optical film piece shown in FIG. 1. [Diagram 3]2 is a schematic cross-sectional view showing a state in which the optical film piece shown in FIG. 1 is integrated with an optical component. FIG. [Figure 4A] 1A-1D illustrate an example of a method for manufacturing an optical film piece according to one embodiment of the present invention. [Figure 4B] This is a continuation of Figure 4A. [Figure 4C] This is a continuation of Figure 4B. [Figure 4D] This is a continuation of Figure 4C. [Diagram 5] FIG. 1 is a schematic diagram showing a general configuration of an example of a display system for VR goggles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In order to clarify the description, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the embodiment, but they are merely examples and do not limit the interpretation of the present invention. In addition, in the drawings, the same or equivalent elements are given the same reference numerals, and duplicate descriptions may be omitted.

[0011] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane retardation measured with light of wavelength λ nm at 23° C. For example, "Re(550)" is the in-plane retardation measured with light of wavelength 550 nm at 23° C. Re(λ) is calculated by the formula: Re(λ)=(nx-ny)×d, where d(nm) is the thickness of the layer (film). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23° C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of wavelength 550 nm at 23° C. Rth(λ) is calculated by the formula: Rth(λ)=(nx-nz)×d, where d(nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is calculated by Nz=Rth / Re. (5)Angle When angles are referred to herein, the angles include both clockwise and counterclockwise angles relative to a reference direction, so for example, "45°" means ±45°.

[0012] [Optical film piece] Fig. 1 is a top view of an optical film piece according to one embodiment of the present invention, Fig. 2 is a schematic partially enlarged cross-sectional view showing the general configuration of the optical film piece shown in Fig. 1, and Fig. 3 is a schematic cross-sectional view showing the state in which the optical film piece shown in Fig. 1 is integrated with an optical component. In Fig. 3, hatching is omitted in the cross sections of the optical component and the optical film piece to make the drawing easier to see. Details of the optical film piece are also omitted.

[0013] The optical film piece 1 includes an absorptive polarizing member 28 and a pressure-sensitive adhesive layer 30. The absorptive polarizing member 28 includes at least an absorptive polarizing film 28a. In the illustrated example, the absorptive polarizing member 28 includes a protective layer 29 in addition to the absorptive polarizing film 28a. Unlike the illustrated example, the protective layer 29 may be omitted. In this case, the absorptive polarizing member 28 may correspond to an absorptive polarizing film.

[0014] The shape of the optical film piece 1 in plan view is substantially circular, but is not limited thereto. For example, the optical film piece 1 may be substantially elliptical or rectangular with rounded corners. The major axis of the optical film piece 1 in plan view is, for example, 10 mm to 100 mm. Here, the major axis in plan view is the distance between the two most distant points on the periphery of the optical film piece when the optical film piece is viewed from above.

[0015] The optical film piece 1 has a first main surface 1a and a second main surface 1b facing each other. The first main surface 1a and the second main surface 1b of the optical film piece 1 have curved surfaces. In the illustrated example, the optical film piece 1 has a convex curvature on the second main surface 1b side, the first main surface 1a has a concave curved surface, and the second main surface 1b has a convex curved surface. In the example shown in FIG. 3, the optical film piece 1 is attached to the concave surface of an optical component (e.g., a lens) L having a curved surface portion by its adhesive layer 30 (not shown in FIG. 3), and the absorptive polarizing film 28a has a convex curvature on the adhesive layer 30 side, and the main surface of the absorptive polarizing film 28a has a curved surface. Unlike the illustrated example, the optical film piece 1 may be attached to the convex surface of the optical component L. The radius of curvature of the main surface of the optical film piece 1 is, for example, 10 mm or more and 150 mm or less, preferably 100 mm or less, and more preferably 90 mm or less. The radius of curvature can be confirmed, for example, by using a laser displacement meter.

[0016] <Absorptive polarizing film> The absorptive polarizing film 28a is typically made of a polyvinyl alcohol resin (PVA resin) containing a dichroic material such as iodine, an organic dye, etc. The thickness of the absorptive polarizing film 28a is, for example, from 1 μm to 20 μm, and may be from 2 μm to 15 μm, 12 μm or less, 10 μm or less, or 8 μm or less.

[0017] The absorptive polarizing film 28a preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The crossed transmittance (Tc) of the absorptive polarizing film 28a is preferably 0.5% or less, more preferably 0.1% or less, and further preferably 0.05% or less. The single transmittance (Ts) of the absorptive polarizing film 28a is, for example, 40.0% to 45.0%, and preferably 41.0% or more. The degree of polarization (P) of the absorptive polarizing film 28a is, for example, 99.0% to 99.997%, and preferably 99.8% or more.

[0018] The crossed transmittance, single transmittance and degree of polarization can be measured, for example, using an ultraviolet-visible spectrophotometer. The degree of polarization P can be calculated from the obtained Tp and Tc by measuring the single transmittance Ts, parallel transmittance Tp and crossed transmittance Tc using an ultraviolet-visible spectrophotometer, using the following formula. Note that Ts, Tp and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. Polarization degree P(%)={(Tp-Tc) / (Tp+Tc)} 1 / 2 ×100

[0019] In the absorptive polarizing film 28a, typically, the polyvinyl alcohol molecules are oriented. The orientation state of the polyvinyl alcohol molecules may be different on the main surface 28b of the absorptive polarizing film 28a. Specifically, the main surface of the absorptive polarizing film 28a may have a distribution of orientation functions that can represent the orientation state of the polyvinyl alcohol molecules. For example, the orientation function of the first portion 28c located at the center of the main surface of the absorptive polarizing film 28a may be different from the orientation function of the second portion 28d located outside the first portion 28c. Specifically, the absolute value of the difference between the orientation function of the first portion 28c and the orientation function of the second portion 28d is, for example, 0.02 or more, and may be 0.05 or more. By having such a relationship, the optical film piece 1 can be suppressed from generating cracks and can have an excellent appearance. In addition, it can be well integrated with the optical component L having a curved surface portion. For example, it can be integrated with the curved surface portion without leaving a gap. Therefore, the optical film piece 1 can achieve, for example, improved visibility and weight reduction of VR goggles.

[0020] The absorptive polarizing film 28a may have a portion (sometimes referred to as a low orientation portion) with a low orientation function on the main surface 28b. For example, the orientation function of the low orientation portion on the main surface 28b of the absorptive polarizing film 28a may be 0.30 or less, 0.29 or less, preferably 0.285 or less, more preferably 0.28 or less, and even more preferably 0.25 or less, and may be 0.22 or less. By having such a portion, the distribution of the orientation function can be satisfied. In addition, the radius of curvature of the main surface of the optical film piece 1 can be reduced. For example, the radius of curvature of the main surface of the optical film piece 1 can be 40 mm or less. Note that when the radius of curvature is more than 40 mm and 70 mm or less, the orientation function of the low orientation portion may be, for example, 0.45 or less, 0.42 or less, 0.40 or less, 0.35 or less, or less than 0.31. When the radius of curvature exceeds 70 mm, the orientation function of the low orientation portion may be 0.50 or less, 0.45 or less, 0.42 or less, or 0.40 or less.

[0021] In one embodiment, the low orientation portion may be formed at the periphery or end of the absorptive polarizing film 28a, while in another embodiment, the low orientation portion may be formed at the center of the absorptive polarizing film 28a.

[0022] A method for producing the polyvinyl alcohol-based resin film (PVA-based resin film) constituting the absorptive polarizing film 28a includes, for example, forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a polyvinyl alcohol-based resin (PVA-based resin) and a halide on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an auxiliary air-stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order, in which the laminate is heated while being transported in the longitudinal direction to cause it to shrink by 2% or more in the width direction.

[0023] The PVA-based resin layer is preferably formed by applying a coating liquid containing a PVA-based resin and a halide to a thermoplastic resin substrate and drying the coating liquid. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin. The thickness of the PVA-based resin layer is preferably 3 to 40 μm, and more preferably 3 to 20 μm.

[0024] Examples of the method for applying the coating liquid include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), etc. The application and drying temperature of the coating liquid is preferably 50° C. or higher.

[0025] From the viewpoint of improving the adhesion between the thermoplastic resin substrate and the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment such as a corona treatment before the PVA-based resin layer is formed, or an easy-adhesion layer may be formed on the thermoplastic resin substrate.

[0026] The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, for example, it may be difficult to form a PVA-based resin layer. If it exceeds 300 μm, for example, in the underwater stretching treatment described below, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.

[0027] The water absorption rate of the thermoplastic resin substrate is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate can absorb water, and the water can act as a plasticizer to plasticize the substrate. As a result, the stretching stress can be significantly reduced, and the substrate can be stretched at a high ratio. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as a significant decrease in the dimensional stability of the substrate during production, which leads to a deterioration in the appearance of the resulting PVA-based resin film. In addition, it is possible to prevent the substrate from breaking during underwater stretching, and the PVA-based resin layer from peeling off from the substrate. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value determined in accordance with JIS K 7209.

[0028] The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120° C. or less. By using such a thermoplastic resin substrate, the stretchability of the laminate can be sufficiently ensured while suppressing the crystallization of the PVA-based resin layer. In consideration of the plasticization of the thermoplastic resin substrate by water and the good underwater stretching, the Tg is more preferably 100° C. or less, and further preferably 90° C. or less. On the other hand, the Tg of the thermoplastic resin substrate is preferably 60° C. or more. By using such a thermoplastic resin substrate, defects such as deformation of the substrate (e.g., generation of unevenness, sagging, wrinkles, etc.) during the coating and drying of the coating liquid can be prevented, and a laminate can be produced well. In addition, the stretching of the PVA-based resin layer can be performed at a suitable temperature (e.g., about 60° C.). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material or by heating using a crystallizing material. The glass transition temperature (Tg) is a value obtained in accordance with JIS K 7121.

[0029] Examples of the thermoplastic resin include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferably used.

[0030] In one embodiment, amorphous (uncrystallized) polyethylene terephthalate resins are preferably used. Among them, amorphous (hard to crystallize) polyethylene terephthalate resins are preferably used. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and / or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.

[0031] In a preferred embodiment, the thermoplastic resin substrate is made of a polyethylene terephthalate resin having an isophthalic acid unit. Such a thermoplastic resin substrate has excellent stretchability and can suppress crystallization during stretching. This is believed to be due to the introduction of an isophthalic acid unit, which gives a large bend to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate with extremely excellent stretchability can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all repeating units. By setting such a content ratio, the crystallinity can be favorably increased in the drying shrinkage treatment described below.

[0032] The thermoplastic resin substrate may be stretched by any appropriate method before forming the PVA-based resin layer. For example, the long thermoplastic resin substrate may be stretched in the transverse direction. The transverse direction is preferably a direction substantially perpendicular to the stretching direction of the laminate described below. The stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C relative to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

[0033] As described above, the coating liquid may contain a PVA resin and a halide. The coating liquid may typically be a solution in which a PVA resin and a halide are dissolved in a solvent. Examples of the solvent include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. Among these, water is preferably used. The concentration of the PVA resin is preferably 3 to 20 parts by weight relative to 100 parts by weight of the solvent. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA resin, and more preferably 10 to 15 parts by weight.

[0034] Examples of the PVA resin include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA resin is, for example, 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined in accordance with JIS K 6726-1994. The average polymerization degree of the PVA resin is, for example, 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be determined in accordance with JIS K 6726-1994. Examples of the halide include iodides such as potassium iodide, sodium iodide, and lithium iodide, and sodium chloride. Of these, potassium iodide is preferably used.

[0035] The coating liquid may contain additives. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants.

[0036] By stretching the PVA-based resin layer, the orientation of the polyvinyl alcohol molecules in the PVA-based resin can be increased, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disturbed and the orientation may be reduced. When a laminate of a thermoplastic resin and a PVA-based resin layer is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin, the tendency of the orientation to be reduced is remarkable. In contrast, by performing high-temperature stretching (auxiliary stretching) in air before stretching a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate in boric acid water, the crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the disturbance of the orientation of the polyvinyl alcohol molecules and the reduction in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of the PVA-based resin film obtained through treatments such as dyeing and underwater stretching in which the laminate is immersed in a liquid.

[0037] In order to obtain high optical properties, a two-stage stretching method may be selected, combining air-stretching (auxiliary stretching) and stretching in boric acid water. By introducing auxiliary stretching, the thermoplastic resin substrate can be stretched while suppressing crystallization, which solves the problem of the thermoplastic resin substrate being excessively crystallized and reduced in stretchability in the subsequent boric acid water stretching, and the laminate can be stretched at a high magnification. In addition, when applying a PVA-based resin onto a thermoplastic resin substrate, it is necessary to lower the application temperature, for example, compared to when applying a PVA-based resin onto a metal drum, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate. As a result, the crystallization of the PVA-based resin becomes relatively low, and a problem of insufficient optical properties cannot be obtained may occur. In contrast, by introducing auxiliary stretching, even when applying a PVA-based resin onto a thermoplastic resin substrate, it is possible to increase the crystallinity of the PVA-based resin, and to achieve high optical properties. At the same time, by increasing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation of the PVA-based resin or dissolution when the resin is immersed in water during subsequent dyeing or stretching processes can be prevented, and high optical properties can be achieved.

[0038] The method of the auxiliary in-air stretching may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds). From the viewpoint of obtaining high optical properties, free-end stretching is preferably used.

[0039] The stretching ratio of the auxiliary air-stretching is preferably 2.0 to 3.5 times. The auxiliary air-stretching may be performed in one stage or multiple stages. When performed in multiple stages, the stretching ratio is the product of the stretching ratios in each stage. The stretching direction in the auxiliary air-stretching is preferably approximately the same as the stretching direction in the underwater stretching.

[0040] The stretching temperature of the auxiliary air stretching is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than Tg+10°C of the thermoplastic resin substrate, and even more preferably equal to or higher than Tg+15°C of the thermoplastic resin substrate. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, the crystallization of the PVA-based resin can be prevented from progressing rapidly, and defects due to crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching) can be prevented. The crystallization index of the PVA-based resin after the auxiliary air stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, the measurement is performed using polarized light as the measurement light, and the crystallization index at 1141 cm of the obtained spectrum is measured. -1 and 1440cm -1 The crystallization index is calculated according to the following formula using the intensity of Crystallization index=(I C / I R ) Here, I C is 1141cm when the measurement light is incident -1 is the intensity of I R is the 1440 cm -1 is the strength.

[0041] After the auxiliary air-stretching treatment, an insolubilization treatment may be carried out before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically carried out by immersing the PVA-based resin layer in an aqueous solution of boric acid. The insolubilization treatment imparts water resistance to the PVA-based resin layer, and can prevent a decrease in the orientation of PVA when immersed in water. The concentration of the aqueous solution of boric acid used in the insolubilization treatment is preferably 1 to 4 parts by weight per 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous solution of boric acid) is preferably 20°C to 50°C.

[0042] The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, the dyeing treatment is performed by allowing the PVA-based resin layer to adsorb iodine. As a method for adsorbing iodine, a method of immersing the PVA-based resin layer (laminate) in a dyeing solution (dyeing bath) containing iodine is preferably adopted.

[0043] The dyeing solution is preferably an aqueous iodine solution. In this case, the amount of iodine is preferably 0.05 to 0.5 parts by weight relative to 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the aqueous iodine solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Among these, potassium iodide is preferably used. The amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, relative to 100 parts by weight of water. The temperature of the dyeing solution during dyeing is preferably 20°C to 50°C in order to suppress dissolution of the PVA resin. When the PVA-based resin layer is immersed in the dye solution, the immersion time is preferably 5 seconds to 5 minutes, and more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

[0044] The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance and polarization degree of the resulting PVA-based resin film are within the above-mentioned ranges. For example, the ratio of the contents of iodine and potassium iodide in the iodine aqueous solution as the dyeing solution is preferably 1:5 to 1:20, more preferably 1:5 to 1:10.

[0045] When a dyeing process is performed continuously after a process (for example, an insolubilization process) in which a laminate is immersed in a treatment bath containing boric acid, the boric acid concentration of the dyeing bath may change over time due to the boric acid contained in the treatment bath being mixed into the dyeing bath, resulting in unstable dyeability. In order to suppress such instability of dyeability, the upper limit of the boric acid concentration of the dyeing bath is adjusted to be preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and even more preferably 0.5 parts by weight, relative to 100 parts by weight of water. In one embodiment, a dyeing bath in which boric acid has been blended in advance is used. This can reduce the rate of change in boric acid concentration when the boric acid of the treatment bath is mixed into the dyeing bath. The amount of boric acid preliminarily mixed into the dye bath (i.e., the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight, and more preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of water.

[0046] After the dyeing process, a crosslinking process may be performed before the underwater stretching process. The crosslinking process is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The crosslinking process imparts water resistance to the PVA-based resin layer, and prevents the orientation of the PVA from decreasing when the layer is immersed in high-temperature water in the subsequent underwater stretching process. The concentration of the aqueous boric acid solution used in the crosslinking process is preferably 1 to 5 parts by weight per 100 parts by weight of water. In addition, when the crosslinking process is performed after the dyeing process, it is preferable to further add an iodide. By adding an iodide, it is possible to suppress the elution of iodine adsorbed to the PVA-based resin layer. The amount of the iodide to be added is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of the iodide are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20°C to 50°C.

[0047] The underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the laminate can be stretched at a temperature lower than the glass transition temperature (typically about 80°C) of the thermoplastic resin substrate or the PVA-based resin layer, and the PVA-based resin layer can be stretched while suppressing its crystallization. As a result, a PVA-based resin film having excellent optical properties can be produced.

[0048] The stretching method of the laminate can be any appropriate method. Specifically, it may be fixed end stretching or free end stretching (for example, a method of uniaxially stretching the laminate by passing it between rolls having different peripheral speeds). Preferably, free end stretching is selected. The stretching of the laminate may be performed in one stage or multiple stages. When performing the stretching in multiple stages, the stretching ratio of the laminate described below is the product of the stretching ratios in each stage.

[0049] The underwater stretching is preferably performed by immersing the laminate in an aqueous solution of boric acid (stretching in boric acid water). By using an aqueous solution of boric acid as a stretching bath, the PVA-based resin layer can be given rigidity that can withstand the tension applied during stretching and water resistance that does not dissolve in water. Specifically, boric acid can generate tetrahydroxyborate anions in the aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer can be given rigidity and water resistance, and can be stretched well, and a PVA-based resin film with excellent optical properties can be produced.

[0050] The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 7 parts by weight, and even more preferably 3 to 6 parts by weight, relative to 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a PVA-based resin film with higher properties can be produced. In addition to boric acid or a borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

[0051] Preferably, an iodide is added to the stretching bath (boric acid aqueous solution). By adding an iodide, it is possible to suppress the elution of iodine adsorbed in the PVA resin layer. Specific examples of the iodide are as described above. The concentration of the iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of water.

[0052] The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C or higher, more preferably 60°C or higher. At such a temperature, the film can be stretched well. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is lower than 40°C, the film may not be stretched well even if the plasticization of the thermoplastic resin substrate by water is taken into consideration. On the other hand, the stretching temperature (liquid temperature of the stretching bath) is preferably 85°C or lower, more preferably 75°C or lower. The higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and the higher the possibility of not obtaining excellent optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0053] The orientation function, breaking point, and elastic modulus of the PVA-based resin film described later can be controlled, for example, by adjusting the stretching ratio in the underwater stretching treatment. In one embodiment, the stretching ratio in the underwater stretching is preferably 1.8 times or less, more preferably 1.7 times or less, and may be 1.6 times or less. The total stretching ratio of the laminate is preferably 4.3 times or less, more preferably 4.0 times or less, and even more preferably 3.7 times or less, relative to the original length of the laminate.

[0054] The stretching ratio in the underwater stretching is, for example, more than 1.0, preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. The total stretching ratio of the laminate is, for example, more than 2.5, preferably 3.0 or more, and more preferably 3.2 or more, relative to the original length of the laminate. With such a stretching ratio, a PVA-based resin film having excellent optical properties can be produced. Such a stretching ratio can be satisfactorily achieved by adopting an underwater stretching method (stretching in boric acid water).

[0055] The drying shrinkage treatment may be performed by zone heating, which heats the entire zone, or by heating the transport roll (using a so-called heating roll). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heat curl of the laminate and produce a PVA-based resin film with excellent appearance. Specifically, by drying the laminate in a state where it is aligned with the heating roll, it is possible to efficiently promote the crystallization of the thermoplastic resin substrate and increase the crystallinity, and even at a relatively low drying temperature, it is possible to satisfactorily increase the crystallinity of the thermoplastic resin substrate. As a result, the rigidity of the thermoplastic resin substrate increases and it becomes in a state where it can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. In addition, by using a heating roll, it is possible to dry the laminate while maintaining it in a flat state, so that it is possible to suppress not only curling but also the occurrence of wrinkles. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction by the drying shrinkage treatment. This is because the orientation of the PVA and the PVA / iodine complex can be effectively increased. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heating roll, the laminate can be continuously shrunk in the width direction while being transported, thereby achieving high productivity.

[0056] For example, the drying conditions can be controlled by adjusting the heating temperature of the transport rolls (temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, etc. The temperature of the heating rolls is preferably 60°C to 120°C, more preferably 65°C to 100°C, and even more preferably 70°C to 80°C. The crystallinity of the thermoplastic resin can be favorably increased, curling can be favorably suppressed, and excellent strength can be imparted to the laminate. The temperature of the heating rolls can be measured by a contact thermometer. Usually, 2 to 40 transport rolls, preferably 4 to 30 transport rolls are used. The contact time (total contact time) between the laminate and the heating rolls is preferably 1 second to 300 seconds, more preferably 1 second to 20 seconds, and even more preferably 1 second to 10 seconds.

[0057] The heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (under room temperature environment). It is preferably provided in a heating furnace equipped with a blowing means. By using drying with a heating roll and hot air drying in combination, it is possible to suppress a steep temperature change between the heating rolls, and it is possible to easily control the shrinkage in the width direction. The hot air drying temperature is preferably 30°C to 100°C. The hot air drying time is preferably 1 second to 300 seconds. The hot air speed is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace, and can be measured by a mini-vane type digital anemometer.

[0058] Preferably, after the underwater stretching treatment and before the drying shrinkage treatment, a washing treatment is performed by, for example, immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0059] For example, the orientation function of the PVA-based resin film may be 0.30 or less, 0.29 or less, preferably 0.285 or less, more preferably 0.28 or less, further preferably 0.25 or less, and may be 0.22 or less. On the other hand, the orientation function is, for example, 0.05 or more, preferably 0.10 or more, more preferably 0.15 or more. If the orientation function is too small, excellent optical properties (for example, single transmittance and / or polarization degree) may not be obtained. Note that the formation of a low orientation portion having the orientation function of more than 0.30 can be achieved, for example, by increasing the stretching ratio by the underwater stretching.

[0060] The absorption axis direction of the PVA-based resin film may substantially correspond to the stretching direction (MD direction) of the PVA-based resin layer. The transmission axis direction of the PVA-based resin film may substantially correspond to the direction (TD direction) perpendicular to the stretching direction (MD direction) of the PVA-based resin layer. The break point of the absorption axis direction of the PVA-based resin film is, for example, 3.0% or more and 20% or less, preferably 3.2% or more. The break point of the transmission axis direction of the PVA-based resin film is, for example, 10% to 50%. The ratio of the break point of the transmission axis direction to the break point of the absorption axis direction of the PVA-based resin film (break point of the transmission axis direction / break point of the absorption axis direction) is, for example, 10 or less, preferably 9 or less. The elastic modulus of the absorption axis direction of the PVA-based resin film is, for example, 1000 MPa or more and 2500 MPa or less, preferably 2200 MPa or less. The elastic modulus of the transmission axis direction of the PVA-based resin film is preferably 1200 MPa to 2500 MPa. The ratio of the elastic modulus in the transmission axis direction to the elastic modulus in the absorption axis direction of the PVA-based resin film (elastic modulus in the transmission axis direction / elastic modulus in the absorption axis direction) is, for example, 0.5 or more, preferably 0.7 or more. Here, the breaking point and elastic modulus of the PVA-based resin film may each be a value at 120°C.

[0061] <Protective layer> The protective layer 29 that can be included in the absorptive polarizing member 28 can be composed of any appropriate film. Examples of materials that are the main components of the film that constitutes the protective layer include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, cycloolefin-based such as polynorbornene, polyolefin-based, (meth)acrylic, acetate-based, and other resins. The resin substrate used in the production of the PVA-based resin film may be used as it is as the protective layer of the absorptive polarizing film.

[0062] The thickness of the protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 50 μm, and further preferably 15 μm to 40 μm.

[0063] The optical film piece 1 can be obtained by integrating the member containing the PVA-based resin film with the curved surface of an optical component (for example, lens L shown in FIG. 3). Specifically, by integrating the member containing the PVA-based resin film with the optical component, an optical film piece 1 including an absorptive polarizing member 28 including an absorptive polarizing film 28a can be obtained. The integration can be typically performed by bonding the member containing the PVA-based resin film with the curved surface of the optical component (for example, lens L) using a pressure-sensitive adhesive layer. The obtained optical film piece 1 can include a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer 30 shown in FIG. 2).

[0064] 4A-4D are diagrams illustrating an example method for making an optical film piece according to one embodiment of the present invention.

[0065] FIG. 4A shows a state in which the work 2 is prepared by providing an adhesive layer or the like on a member including a PVA-based resin film, and the work 2 is placed above the lens L, which is an adherend. The lens L is, for example, circular in plan view and has a concave shape in cross section. The radius of curvature of the curved surface of the lens L is, for example, 10 mm or more and 150 mm or less, preferably 100 mm or less, more preferably 90 mm or less, and may be 70 mm or less, or may be 40 mm or less. The work 2 is placed at a predetermined distance from the concave surface (upper surface) of the lens L. The lens L is placed on a holding portion 52 on a holding table 51 that can be raised and lowered and is housed in the lower chamber 50. The end portion 2a of the work 2 is sandwiched between the upper chamber 60 and the lower chamber 50.

[0066] 4B shows a state in which the space in which the workpiece 2 is placed is depressurized and the workpiece 2 is heated. Specifically, the upper chamber 60 and the lower chamber 50 are depressurized by a vacuum device (not shown) and then the workpiece 2 is heated. The shape of the workpiece 2 may be easily deformed by heating. The heating temperature of the workpiece 2 is preferably 50°C or higher and 150°C or lower.

[0067] FIG. 4C shows a state where the work 2 starts to be bonded to the lens L. When the work 2 becomes easily deformed, the holding table 51 is raised and a part of the lens L (in the illustrated example, the peripheral part) is brought into contact with the work 2. After the contact, the air pressure in the upper chamber 60 is gradually increased. The air pressure in the upper chamber 60 becomes higher than the air pressure in the lower chamber 50, and a pressure difference may occur between the two spaces. Due to this pressure difference, the work 2 is gradually drawn downward, and the entire surface of the work 2 may be bonded to the lens L as shown in FIG. 4D. In the illustrated example, after the peripheral part of the lens L is brought into contact with the work 2, the work 2 may be bonded from the peripheral part to the center of the lens L. After the bonding, unnecessary parts of the work 2 (for example, parts that do not overlap with the lens L in a plan view) are removed, and an optical film piece 1 as shown in FIG. 3 can be obtained.

[0068] When integrated with the curved surface portion, the PVA-based resin film can be stretched. The orientation of the PVA-based resin film can change by being stretched. For example, the orientation of the PVA-based resin film can be increased by being stretched. In the example shown in FIG. 4, the work 2 (PVA-based resin film) can be stretched more from the periphery (end) of the lens L to the center. For example, by using a PVA-based resin film that satisfies the above-mentioned orientation function, integration with the curved surface portion can be performed well. Specifically, the member including the PVA-based resin film can be made to conform to the shape of the curved surface portion, and can be integrated with the curved surface portion without leaving any gaps. In addition, defects such as cracks occurring in the PVA-based resin film can be suppressed when integrating with the curved surface portion.

[0069] The optical film piece according to the embodiment of the present invention may include any suitable other optical element in addition to the absorptive polarizing element. The optical film piece may be used in any suitable display. For example, the optical film piece may be suitable for use in VR goggles.

[0070] [Display System] FIG. 5 is a schematic diagram showing an outline of an example of a display system of VR goggles, and shows the arrangement and shape of each component of the display system. The display system 10 includes a display element 12, a reflective polarizing member 14, a first lens unit 16, a half mirror 18, a first λ / 4 member 20, a second λ / 4 member 22, and a second lens unit 24. The reflective polarizing member 14 is disposed in front of the display surface 12a of the display element 12, and can reflect light emitted from the display element 12. The first lens unit 16 is disposed on the optical path between the display element 12 and the reflective polarizing member 14, and the half mirror 18 is disposed between the display element 12 and the first lens unit 16. The first λ / 4 member 20 is disposed on the optical path between the display element 12 and the half mirror 18, and the second λ / 4 member 22 is disposed on the optical path between the half mirror 18 and the reflective polarizing member 14.

[0071] The half mirror, or the components arranged forward from the first lens portion (in the illustrated example, the half mirror 18, the first lens portion 16, the second λ / 4 member 22, the reflective polarizing member 14, and the second lens portion 24) may be collectively referred to as the lens portion (lens portion 4).

[0072] The display element 12 is, for example, a liquid crystal display or an organic EL display, and has a display surface 12a for displaying an image. The light emitted from the display surface 12a passes through, for example, a polarizing member that may be included in the display element 12, and is converted into a first linearly polarized light.

[0073] The first λ / 4 member 20 can convert the first linearly polarized light incident on the first λ / 4 member 20 into the first circularly polarized light. The first λ / 4 member 20 may be provided integrally with the display element 12.

[0074] The half mirror 18 transmits the light emitted from the display element 12 and reflects the light reflected by the reflective polarizing member 14 toward the reflective polarizing member 14. The half mirror 18 is provided integrally with the first lens portion 16.

[0075] The second λ / 4 member 22 can transmit the light reflected by the reflective polarizing member 14 and the half mirror 18 through the reflective polarizing member 14. The second λ / 4 member 22 may be provided integrally with the first lens portion 16.

[0076] The first circularly polarized light output from the first λ / 4 member 20 passes through the half mirror 18 and the first lens portion 16, and is converted into the second linearly polarized light by the second λ / 4 member 22. The second linearly polarized light output from the second λ / 4 member 22 is reflected toward the half mirror 18 without passing through the reflective polarizing member 14. At this time, the polarization direction of the second linearly polarized light incident on the reflective polarizing member 14 is the same as the reflection axis of the reflective polarizing member 14. Therefore, the second linearly polarized light incident on the reflective polarizing member 14 is reflected by the reflective polarizing member 14.

[0077] The second linearly polarized light reflected by the reflective polarizing member 14 is converted into the second circularly polarized light by the second λ / 4 member 22, and the second circularly polarized light emitted from the second λ / 4 member 22 passes through the first lens unit 16 and is reflected by the half mirror 18. The second circularly polarized light reflected by the half mirror 18 passes through the first lens unit 16 and is converted into the third linearly polarized light by the second λ / 4 member 22. The third linearly polarized light passes through the reflective polarizing member 14. At this time, the polarization direction of the third linearly polarized light incident on the reflective polarizing member 14 is the same as the transmission axis of the reflective polarizing member 14. Therefore, the third linearly polarized light incident on the reflective polarizing member 14 passes through the reflective polarizing member 14.

[0078] The light transmitted through the reflective polarizing member 14 passes through the second lens portion 24 (the absorptive polarizing member 28 and the second lens portion 24) and enters the eye 26 of the user.

[0079] The absorption axis of the polarizing member included in the display element 12 and the reflection axis of the reflective polarizing member 14 may be disposed approximately parallel to each other or approximately perpendicular to each other. The angle between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the first λ / 4 member 20 is, for example, 40° to 50°, may be 42° to 48°, or may be about 45°. The angle between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the second λ / 4 member 22 is, for example, 40° to 50°, may be 42° to 48°, or may be about 45°.

[0080] The in-plane retardation Re(550) of the first λ / 4 member 20 is, for example, 100 nm to 190 nm, and may be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. The first λ / 4 member 20 preferably exhibits an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light. The Re(450) / Re(550) of the first λ / 4 member 20 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0081] The in-plane retardation Re(550) of the second λ / 4 member 22 is, for example, 100 nm to 190 nm, and may be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. The second λ / 4 member 22 preferably exhibits an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light. The Re(450) / Re(550) of the second λ / 4 member 22 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0082] The display system 10 may include an absorptive polarizing member 28. The absorptive polarizing member 28 may be disposed in front of the reflective polarizing member 14. The reflection axis of the reflective polarizing member 14 and the absorption axis of the absorptive polarizing member 28 (absorptive polarizing film 28a) may be disposed approximately parallel to each other, and the transmission axis of the reflective polarizing member 14 and the transmission axis of the absorptive polarizing member 28 (absorptive polarizing film 28a) may be disposed approximately parallel to each other. The reflective polarizing member 14 and the absorptive polarizing member 28 may be integrated together. The absorptive polarizing member 28 may be used in the above-mentioned display system, for example, from the viewpoint of improving visibility.

[0083] In the display system 10, a space may be formed between the first lens portion 16 and the second lens portion 24. In this case, it is preferable that the member disposed between the first lens portion 16 and the second lens portion 24 is integrally provided with either the first lens portion 16 or the second lens portion 24. For example, the member disposed between the first lens portion 16 and the second lens portion 24 is integrated with either the first lens portion 16 or the second lens portion 24 via an adhesive layer. According to such a configuration, for example, each member may be excellent in handleability. The adhesive layer may be formed of an adhesive or a pressure-sensitive adhesive. Specifically, the adhesive layer may be an adhesive layer or a pressure-sensitive adhesive layer. The thickness of the adhesive layer is, for example, 0.01 μm to 60 μm.

[0084] The optical film piece according to the embodiment of the present invention may include, for example, the components provided in the display system. The optical film piece may include other components such as an adhesive layer for integrating adjacent components. The thickness of the optical film piece may vary depending on the type and number of components included, and may be, for example, 50 μm to 400 μm.

[0085] For example, the optical film piece according to the embodiment of the present invention may include a reflective polarizing member 14. The optical film piece may also include a second λ / 4 member 22. The optical film piece may be integrated with, for example, the first lens portion 16 or the second lens portion 24. Typically, the optical film piece may be bonded to the first lens portion 16 or the second lens portion 24, which is an adherend, via an adhesive layer. For example, the first lens portion 16 shown in FIG. 5 has a curved portion and may correspond to the optical component (lens L) described above. EXAMPLES

[0086] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The thickness, orientation function, single transmittance and polarization degree are values ​​measured by the following measurement methods. <Thickness> The thickness of 10 μm or less was measured using a scanning electron microscope (manufactured by JEOL, product name "JSM-7100F"), and the thickness of more than 10 μm was measured using a digital micrometer (manufactured by Anritsu, product name "KC-351C"). <Orientation function> A Fourier transform infrared spectrometer (PerkinElmer, model "Frontier FT-IR") was used to measure the spectra of the measurement samples (PVA-based resin film and absorptive polarizing film) using polarized light as the measurement light and attenuated total reflection spectroscopy (ATR), and the orientation function of the measurement sample (PVA orientation) was calculated from the obtained spectral results. Specifically, germanium was used as the crystallite to which the measurement sample was to be adhered, the angle of incidence of the measurement light was set to 45°, and the incident polarized infrared light (measurement light) was polarized light (s-polarized light) that vibrated parallel to the surface of the germanium crystal to which the sample was to be adhered. Measurements were performed with the stretching direction of the measurement sample arranged parallel and perpendicular to the polarization direction of the measurement light, and the 2941 cm -1 The intensity was calculated according to the following formula: -1 is used as the reference peak, and 2941 cm -1 / 3330cm -1 The value is 2941 cm. Note that f=1 is perfect alignment, and f=0 is random. -1 The peak is considered to be an absorption due to vibration of the main chain (-CH2-) of PVA in the measurement sample. f=(3 <cos 2 θ>-1) / 2 =(1-D) / [c(2D+1)] =-2×(1-D) / (2D+1) where c=(3cos 2 β-1) / 2, 2941cm -1 For vibration, β=90°. θ: Angle of molecular chain to stretching direction β: Angle of the transition dipole moment with respect to the chain axis D = (I⊥) / (I / / ) (In this case, the more the PVA molecules are oriented, the larger D becomes.) I⊥: Absorption intensity when the polarization direction of the measurement light and the stretching direction of the measurement sample are perpendicular I / / : Absorption intensity when the polarization direction of the measurement light is parallel to the stretching direction of the measurement sample <Single unit transmittance and polarization degree> For the laminates of PVA-based resin film / resin substrate obtained in the examples and comparative examples, the single transmittance Ts, parallel transmittance Tp, and cross transmittance Tc measured using an ultraviolet-visible spectrophotometer (LPF200, manufactured by Otsuka Electronics Co., Ltd.) were taken as Ts, Tp, and Tc of the PVA-based resin film, respectively. These Ts, Tp, and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. The degree of polarization P was calculated from the obtained Tp and Tc using the above formula.

[0087] [Example 1] (Formation of PVA resin film) The thermoplastic resin substrate was a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of about 75° C. One side of the resin substrate was subjected to a corona treatment. A PVA aqueous solution (coating liquid) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin made by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, product name "GOHSENEX Z410") in a ratio of 9:1, and dissolving the mixture in water. The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. The obtained laminate was uniaxially stretched at its free end to 2.4 times its original size in the machine direction (longitudinal direction) between rolls with different peripheral speeds in an oven at 130° C. (auxiliary air stretching treatment). Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment). Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the final polarizing film would be 40.0% or more (dyeing process). Next, the piece was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment). Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4% by weight, potassium iodide concentration: 5% by weight) at a liquid temperature of 70°C and uniaxially stretched in the longitudinal direction (longitudinal direction) by 1.46 times (total stretching ratio: 3.5 times) between rolls with different peripheral speeds (underwater stretching treatment). Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment). Thereafter, while drying in an oven maintained at 90°C, it was brought into contact with a SUS heated roll whose surface temperature was maintained at 75°C for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 2%. In this manner, a PVA-based resin film having a thickness of 7 μm, an orientation function of 0.24, a single-unit transmittance Ts of 41.5%, and a polarization degree P of 99.9% was formed on the resin substrate.

[0088] (Workpiece creation) An acrylic adhesive composition was applied to the PVA resin film side of a laminate of a resin substrate and a PVA resin film, and then dried to form an adhesive layer with a thickness of 40 μm, thereby obtaining a workpiece.

[0089] [Example 2] In the preparation of the absorptive polarizing member, the stretching ratio in the underwater stretching process was 1.67 times (total stretching ratio was 4.0 times), and an absorptive polarizing film with a thickness of 7 μm, an orientation function of 0.28, a single transmittance Ts of 41.2%, and a polarization degree P of 99.9% was formed. A workpiece was obtained in the same manner as in Example 1.

[0090] [Example 3] In the preparation of the absorptive polarizing member, the stretching ratio in the underwater stretching process was 1.25 times (total stretching ratio was 3.0 times), and an absorptive polarizing film with a thickness of 7 μm, an orientation function of 0.20, a single transmittance Ts of 41.8%, and a polarization degree P of 99.9% was formed. A workpiece was obtained in the same manner as in Example 1.

[0091] [Comparative Example 1] In the preparation of the absorptive polarizing member, the stretching ratio in the underwater stretching process was 1.88 times (total stretching ratio was 4.5 times), and an absorptive polarizing film with a thickness of 6 μm, an orientation function of 0.31, a single transmittance Ts of 40.9%, and a polarization degree P of 99.9% was formed. A workpiece was obtained in the same manner as in Example 1.

[0092] [Comparative Example 2] In the preparation of the absorptive polarizing member, the stretching ratio in the underwater stretching process was set to 2.3 times (total stretching ratio was 5.5 times), and an absorptive polarizing film having a thickness of 5 μm, an orientation function of 0.39, a single transmittance Ts of 40.5%, and a polarization degree P of 99.9% was formed. A workpiece was obtained in the same manner as in Example 1.

[0093] The PVA-based resin films and workpieces of each of the Examples and Comparative Examples were evaluated as follows. The evaluation results are summarized in Table 1 together with the orientation function and optical properties of the PVA-based resin films. <Evaluation> 1. Breaking point and elastic modulus of PVA resin film The obtained PVA-based resin film was punched out using a blade of 150 mm (long side) × 25 mm (short side) to obtain a rectangular measurement sample. The punching was performed so that the long side was aligned along the MD direction (absorption axis direction) and the long side was aligned along the TD direction (transmission axis direction). The obtained measurement sample was chucked in a tensile tester (Shimadzu Corporation, "Autograph AG-Xplus") with a chucking distance of 80 mm, and heated to 120°C. After leaving it to stand for 1 minute in this state, it was pulled in the long side direction at a pulling speed of 0.8 mm / min while being heated to 120°C, and the change in stress with respect to the pulling distance was measured. The elastic modulus (tensile elastic modulus) was calculated from the slope of the initial line (strain (pulling distance / chucking distance): stress line at 0.050% to 0.250%) in the obtained stress-strain curve. In addition, the point where the stress suddenly drops was calculated as the breaking point. 2. Sticking the workpieces together As shown in Figures 4A to 4D, the obtained workpiece was bonded to the curved surface (concave surface) of a lens with a diameter (major axis) of 50 mm and a curvature radius of 35 mm at 120°C several times. The occurrence of cracks, bonding defects, etc. during bonding was checked. 3. Orientation function distribution of absorptive polarizing film The orientation function was measured for an optical film piece (absorptive polarizing film) obtained by bonding the workpiece to the curved surface of the lens. Specifically, the optical film piece was peeled off from the lens, and test pieces measuring 10 mm x 10 mm were cut out from the center and periphery, and these were used for measurement. The test pieces were cut so that one side was parallel to the absorption axis of the absorptive polarizing film. The method for measuring the orientation function is as described above.

[0094] [Table 1]

[0095] In Examples 1, 2, and 3, the workpiece could be bonded to the curved surface of the lens while suppressing the occurrence of cracks. On the other hand, in Comparative Example 1, the workpiece could be bonded to the lens, but many cracks occurred during bonding. In Comparative Example 2, the workpiece could not be bonded to the lens. Specifically, the workpiece did not stretch, and a gap occurred between the lens and the workpiece. The cracks tended to occur along a direction approximately perpendicular to the absorption axis direction (the stretching direction of the PVA-based resin layer).

[0096] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the above-described embodiment may be replaced with a configuration that is substantially the same as the configuration shown in the above-described embodiment, a configuration that provides the same action and effect, or a configuration that can achieve the same purpose. [Industrial Applicability]

[0097] Optical film pieces according to embodiments of the present invention can be used in displays such as VR goggles. [Explanation of symbols]

[0098] 1 piece of optical film 10 Display System 12 Display element 14 Reflective polarizing element 16 First lens section 18 Half Mirror 20 First λ / 4 member 22 Second λ / 4 member 24 Second lens section 28 Absorption type polarizing element 28a Absorption type polarizing film 28b Main surface 28c First part 28d Second part 29 Protective layer 30 Adhesive layer

Claims

1. An optical film piece comprising an absorptive polarizing film, the absorptive polarizing film is made of a polyvinyl alcohol-based resin, On a main surface of the absorptive polarizing film, an orientation function of a first portion located in a central portion is different from an orientation function of a second portion located outside the first portion. Optical film piece.

2. The optical film piece according to claim 1 , wherein the absorptive polarizing film has a portion having an orientation function of 0.30 or less.

3. The optical film piece of claim 1 , wherein an absolute value of a difference between the orientation function of the first region and the orientation function of the second region is 0.02 or more.

4. The optical film piece of claim 1 , wherein the major surface has a curved surface.

5. A method for producing an optical film piece according to claim 1, comprising the steps of: The method includes heating and stretching a member including a polyvinyl alcohol-based resin film to integrate the member with a part having a curved surface, The orientation function of the polyvinyl alcohol-based resin film is 0.30 or less. A method for making an optical film piece.

6. The method for manufacturing an optical film piece according to claim 5 , wherein the radius of curvature of the curved surface of the component is 150 mm or less.

7. The method for producing an optical film piece according to claim 5 , wherein the radius of curvature of the curved surface of the component is 40 mm or less.

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